Process for the production of silicofluorides



Patented June 18, 1935 UN IT E i PROCESS FOR THE PRODUCTION OF SILICQFLUORIDES Emil Gotthilf Leopold Abel, Brand-Erbisdorf,

Germany, assignor to Brander Farbwerke, Chemische Fabrik Geselischatt mit beschrankter Haftung, Brand-Erbisclorf, Germany, a corporation of Germany No Drawing. Application August 15, 1932, Serial No. 628,896. In Germany August 2 1931 2 Claims. (o1; 2s-ss) The invention relates to a process for the prothe form of powder, is added. After that the duction of silicofiuorides,-such, for example, as equivalent quantity of zinc dust, which is dry, or are used for tin1ber-preserving,--and is particumixed with a small quantity of water--in'order to larly adapted to the production of silicoiiuorides avoid the formation of lumps-is added, under of the metals, as zinc and the like. stirring. It is stirred until all the zinc-metal has i 5 It is well known, that the salts of silicofluoric reacted, which can be recognized by the ceasing acid, particularly the silicofluoride of zinc, are exof the formation of hydrogen-gas. The catalyser, cellent products for preserving wood. But they although being metallic and possessing a capacity have a great quantity of acid which is unbound. for reaction, does not react with the silicofiuoric For that reason they have a destroying effect on acid andcan therefore be employed again in the 10 metals-especially iron-so that they can notbe next charge, alter having been separated from used for the impregnation of Wood in pressure the solution of silicofluoride of zinc.

chamber installations, and for that reason they It is evident that the process, in accordance have hitherto played but a. subordinate part in With the invention, may be varied by supplying the technique of impregnating. the acid first and the zinc-dust afterwards, the 15 As a rule, for example, silicofluoride of zinc is mass of catalyzer', which may be in a swelled-up produced by dissolving shavings of zinc in condition, being added last. stoicheioinetrical relation in silicofluoric acid. Al- In view of the comp discussion above with though the process may be very simple, it has regard to the making of the silicofiuoride of zinc, nevertheless its difficulties and shows great disit will be obvious to persons skilled in the art how advantages. The complete reaction of the zincto make silicofluorides of other metals. metal requires an unproportionally long time. The following experiments may serve to illus- In spite of the fact that the metal and the acid trate the technical and economical advantages of do react with each other in equivalent quantities, the present invention. It may suffice, for the the process does not react quantitatively. Durpurposes of these experiments, to choose reduced 25 ing the reaction of the metal upon the acid, a copper as the catalyzer. state of equilibrium arises, so that undissolved zinc and unbound acid remain after the reac- Example Iflwlmout camzyszs tion, whereby the solution-or the salt produced There were combined together, under constant by concentration, respectively-becomes useless stirring, 131 grams of d, Scrap Z in a l- 30 as a means of impregnating in chamber installachip form, with 348 grams of fluosilicic acid, at tions. degrees Be (34 per-cent). The temperature A further disadvantage of the known processes rose to ab ut 37 de r e and though the reaclies in the fact that the reaction must be carried tion was quite intense, at first, it abated rapidly. 35 out in a solution considerably diluted with wa- One and one-half hours later, therefore, 100 35 ter, in order to accelerate the process. cubic centimeters of water was added. After v The invention avoids these disadvantages. It twenty hours, the Solution w found to have a was found that, when producing silicofluorides, density of 42 degrees Be. It was remarkably acid. extremely pure terminal lye, being absolutely free A further 100 cubic centimeters of water was then 40 from acid, is obtained by carrying out the reacadded and, after w y X hours, was again 40 tion in the presence of a catalyser. Zinc metal, tested, and was found to have a density of 41 for instance,-'particularly in the shape of zincdegrees Be. Twenty four hours later, still andust, reacts upon acid in an extraordinary other 100 cubic centimeters of water was added;

short time by bringing the equivalent quantity of after seventy two further hours, it was found, on

45 a metallic catalyser-as, for example, copper retest, to have a density of 38 degrees B. This 4 duced and finely precipitated-into the very lazy time, cubic centimeters of water was introreaction mixture. The process then becomes duced; and, as no further observable reaction folquantitative according to the equation: lowed, the experiment was terminated, and the resulting composition analyzed. There were Zn+s1HzF6+Cu ZnS1F6+2H+Cu' 1743 grams of very acid liquor of 26 degrees Be, 50

The process in accordance with the invention containing 556.7 grams ZYISiFfi-l-GHZO, counting can, for example, be carried out as follows: in the free acid, which also spindles high. This The quantity of silicofluoric acid necessary for would correspond to a yield of 88.22 per cent.

one charge is brought into the vessel and then The undissolved zinc metal residue amounted,

the equivalent quantity of reduced copper, in after drying, to 38.22 per cent of the originally Experiment No. II-without catalysis This experiment, employing zinc chips, Without a catalyzer, was repeated, with the only difference that the time of reaction was increased to seven weeks. Since, after the lapse-of this time, no further reaction could be observed, the experiment was terminated and the results analyzed. There were found 813 grams of liquor of 28 degrees B. (279.67 grams ZnSiFs+6HzO and 408 grams liquor of 0.5 degree B. (2.5 grams ZnSiFs+6HzO), or a total of 282.17 grams of ZnSiF6+6HzO. This corresponded to 99.42 per cent of the amount that should have been ob tained theoretically if the acid being also spindled and not subtracted is included. The liquor was strongly acid. The undissolved zinc residue, when dry, weighed 35.4 grams, which corresponded to 2'7 per cent of the zinc quently gave a yield of 73 Experiment No. IIIwithout catalysis The same experiment, with the same metal, without the use of a catalyzer, was again repeated, but permitting the reaction to take place for only six hours. The results were 7'74 grams liquor, at 41.5 degrees B. and 661 grains liquor, at 14.5 degrees B., or a total of 1,435 grams liquor, at 29.5 B., corresponding to 520.097 grams ZnSiF6+6H2O including the free acid not being saturated,

This product was very strongly acid, and an analytic determination of the end product of the above-mentioned weight showed an acid content of, together, 139.568 grams of the fluo-silicic acid per cent) which, on the other hand. corresponded to 400.47 grams of acid of 35 degrees B. It follows that 48.40 per cent of the originally added acid was not utilized; which checks exactly, for the residue of the zinc sheet, well washed and well dried, weighed 64.5 grams, corresponding to 48.48 per cent of the zinc metal originally employed.

The yield, according to this experiment, therefore, was about 51.5 per cent.

These three experiments have been carried out with sheet zinc, instead of with zinc dust, in order to demonstrate that the catalytic action of old zinc is quite insufiicient for producing a neutral end product. The solution of the metal when the catalyzer is employed yields, in a fraction of the time formerly necessary, a nearly quantitative gain without residue, and the end product is fully neutral.

As opposed to this, the experiments based upon the prior-art processes involve an uncommonly long time of reaction and a thoroughly unsatisfactory result, for substantial residues of the metallic zinc are left behind and the end products of the resulting mass are strongly acid, in which condition they are useless.

employed. This conseper cent.

Two experiments in accordance with the present invention, Nos. IV and V, will now be recounted, the first using scrap zinc, and the other zinc dust; the catalyzer used during the reaction, in both cases, as before suggested, being reduced copper.

Experiment No. IVusing the catalyzer The following are mixed together, while stirring: 131 grams zinc chips, as before, 848 grams fluo-silicic acid, at 35 degrees B. (34 per cent), grams of the catalyzer, moistened with 330 grams water, and 100 grams water as the diluent. After twenty four hours, during which the mixture is frequently stirred, the experiment is ended, and the products analyzed. There results: 671 grams liquor of 44 degrees Be. (333.54 grams znem -enzo), and 2,400 grams liquor of 10 degrees B. (294.864 grams ZnSiFe+6I-I2O), a total of 628.404 grams, or a gain of 99.58 per cent.

The residue of undissolved zinc consists only of traces, and the liquor in whichit is contained is fully neutral.

Experiment No. V using the catalyzer The same experiment is repeated, but with dififerent proportions and using zinc dust. The following ingredients are employed, in the following proportions: 300 grams zinc dust, 300 grams catalyzer, 200 grams water for moistening the catalyzer, and 2,000 grams fluo-silicic acid, at 35 degrees B. The experiment starts at noon, when the temperature of a very strong reaction rises to 85 degrees C., which shows how rapid is the chemical action. Barely half an hour later, the reaction is completed, for the mixture has come fully to rest, and test with Congo red paper shows the solution to be entirely neutral. total liquor containing also the washing water weighs 5,205 grams with a density of 25 degrees Be. Analysis of the free acid yields a content of 0.1.96 per cent in weight of free, one-hundredper-cent, silico-fluoric acid, which shows that all the added zinc dust has been dissolved. The catalyzer, remaining behind and being always ready for repeated use, weighs exactly 300 grams, so that there can not be present any undissolved zinc or any free acid.

What I claim is:

1. A process for the production of silicofiuorides out of fluo-silicic acid, particularly for the use of timber preserving, characterized by the fact of carrying out the reaction of fluosilicic acid upon zinc metal in the presence of reduced copper as catalyzer.

2. A process for the production of silicofiuorides out of fiuo-silicic acid, particularly for the use of timber preserving, characterized by the fact of carryingout the reaction of fluo-silicic acid upon zinc metal in the presence of reduced copper as catalyzer, the copper being present in a quantity equal to the chemical equivalent of the zinc metal.

EMIL GOTTHILF ABEL.

The 

